The present invention relates generally to aircraft gas turbine engines, and, more specifically, to a high bypass turbofan engine having a fan thrust reverser.
High bypass turbofan gas turbine engines are commonly used for powering an aircraft in flight. The turbofan engine includes a core engine surrounded by a core cowl for powering a fan disposed upstream therefrom. A nacelle surrounds the fan and a portion of the core engine and is spaced therefrom to define an annular bypass duct, with the nacelle having a fan inlet at a forward end thereof and a fan outlet or nozzle at an aft end thereof defined around the core cowl.
Disposed in the aft section of the fan nacelle is a conventional fan thrust reverser for reversing thrust upon landing of the aircraft to enhance its stopping capability. The fan thrust reverser is typically mounted between an axially translatable aft cowl and a stationary forward cowl. A plurality of thrust reversing deflector doors are mounted around the inner perimeter of the aft cowl and are typically deployed by various linkages and actuators as the aft cowl translates aft when required. The deflector doors block bypass flow and divert it radially outwardly through conventional cascade turning vanes mounted between the forward and aft cowls which deflect the bypass flow in a forward direction for reversing thrust. The cascade vanes are uncovered when the aft cowl is deployed and are covered when the aft cowl is stowed.
Although the fan nozzle is necessarily repositioned upon axial translation of the aft cowl during deployment of the thrust reverser, it is then inoperative since the bypass flow is diverted through the cascade vanes. When the thrust reverser is stowed, the fan nozzle provides a fixed discharge flow area of the bypass duct which is typically preselected for maximizing efficiency of the turbofan engine at a given design point such as cruise operation of the aircraft in flight. Variable area operation is therefore not possible with a conventional fan thrust reverser. However, variable area fan nozzles are known in the art and are effective for providing enhanced performance of turbofan engines by allowing adjustments in discharge area depending upon required operating conditions. However, conventionally known variable area fan nozzles are relatively complex and would substantially add to the complexity of the fan nacelle in the area of the required thrust reverser due to the attendant separate nozzle flaps and actuators required therefor.